1. Field of the Invention
This invention relates to a printing device for printing a still picture, such as a picture formed by a video camera or a still television picture, using a vaporized dye, and a photographic paper on which printing is made by such printing device.
2. Description of the Related Art
There has hitherto been known a printing device, such as a sublimation printer, in which a sublimation ink ribbon, coated with a sublimable dye, is superposed on the photographic paper, and an electric energy corresponding to the picture information is applied to a thermal head for subliming the dye on the ink ribbon under a heat energy supplied from the thermal head for transcribing the sublimed dye onto the photographic paper.
The sublimation ink ribbon is prepared by dissolving a sublimable dye in e.g. a solution of acetate or polyester and adding a dispersant to the resulting solution to form a colloidal solution in the form of an ink which is mixed with a binder and subsequently coated on a base paper.
The photographic paper usually has a receptor layer of a heat transfer recording material on a photographic base paper. Among the heat transcription recording materials in current use is a dye-like resin, such as polyester or polycarbonate resin, admixed with a lubricant.
The thermal head is a device which translates an electrical energy into a heat energy, that is a device in which the dye is sublimed from the sublimation ink ribbon under the Joule's heat generated on flowing the current through a resistor for transcribing the sublimed dye onto the photographic paper.
When the recording picture is formed on the photographic paper by the above-mentioned sublimation ink ribbon and thermal head, the receptor layer of the photographic paper undergoes the following changes:
That is, when the heat energy is applied from the thermal head, the polyester resin, for example, of the receptor layer undergoes glass transition and softening and thereby turned into the liquid, at the same time that the dye in the sublimation ink ribbon is transferred onto the receptor layer so as to be dissolved or dispersed in the layer to form the recording picture.
With the above-described sublimation printer, in which printing is made on the photographic paper using the sublimation ink ribbon and the thermal head, it is necessary to provide an ink ribbon takeup mechanism for rewinding the ink ribbon and a heat radiating mechanism for the thermal head. On the other hand, the thermal head usually has a heat conversion efficiency of not higher than 10%, thus leading to considerable power consumption. Thus it has been difficult with the conventional sublimation type printer to realize saving in power and reduction in size and costs.
On the other hand, the sublimation ink ribbon can be used only once for each picture and hence is not economically desirable. Besides, the used-up ink ribbon cassette can not be regenerated and hence is to be discarded in a manner of not destroying the earth's environment.
Besides, the printing by such printing device is carried out by stacking dyes of yellow (Y), magenta (M) and cyan (C), so that it becomes necessary to perform three cycles of the complicated and time-consuming operations of feeding the ink ribbon, vertically moving the thermal head and feeding the photographic paper.
The thermal head generally has the line-head structure of thin resistors generated by sputtering being arranged in a line, thus the size of the printing paper cannot be set freely.
Since it is generally desirable to heat the receptor layer on the photographic paper when subliming and transcribing the sublimable dye onto the photographic paper by the thermal head, it has been a conventional practice to increase the thrusting force of the thermal head to raise the tightness of contact between the ink ribbon and the photographic paper and to apply heat to the receptor layer of the photographic paper by the thermal head. It should be noted that, if the force of thrusting the thermal head to the ink ribbon and the photographic paper is increased, the driving force necessary for the movement of the thermal head, rewinding of the ink ribbon and the feed of the photographic paper has to be correspondingly increased. In addition, since the ink ribbon is prepared by coating the dye processed into an ink on the base paper, as described above, the heat reaches the receptor layer via the base paper and the dye layer. Besides, since air layers tend to be produced between the respective layers, the heat to be applied to the receptor layer needs to be set to take account of heat losses produced in each layer, thus lowering the heat efficiency.
On the other hand, the produced picture tends to be lowered in quality if the photographic paper is not whitened at least directly after printing.